Vulcanization of epihalohydrin polymers

ABSTRACT

EPIHALOHYDRIN POLYMERS, OR EPIHALOHYDRIN POLYMERSULFUR CURABLE RUBBER SYSTEMS, ARE VULCANIZED IN THE PRESENCE OF A NOVEL CROSS-LINKING FORMULATION CONSISTING ESSENTIALLY OF (1) BASIC LEAD SULFATE SULFITE, (2) AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF 2-MERCAPTOIMIDAZOLINESS, 2-MERCAPTOPYRIMIDES, AND THIOUREAS, AND (3) SULFUR, IF RUBBER IS PRESENT.

y 2, 1974 HIROSHI HAN! ETAL 3,822,241

VULCANIZATION OF EPIHALOHYDRIN POLYMERS Original Filed June 5, 1970' TORQUE (kg cm) CROSS-LINKING TIME (min.)

United States Patent Office 3,822,241 Patented July 2, 1974 3,822,241 VULCANIZATION OE EPIHALOHYDRIN POLYMERS Hiroshi Hani, Bunji Amemiya, Ginnosuke Tanaka, Hiroshi Kawahara, and Minoru Yamada, Kanagawa-ken, Japan, assignors to Asahi Glass Co., Ltd., Tokyo, Japan Original application June 5, 1970, Ser. No. 43,691, now Patent No. 3,700,650. Divided and this application June 8, 1972, Ser. No. 261,040

Int. Cl. C08c 17/28; C08d 13/28; C08g 30/10 US. Cl. 260-79 9 Claims ABSTRACT OF THE DISCLOSURE Epihalohydrin polymers, or epihalohydrin polymersulfur curable rubber systems, are vulcanized in the presence of a novel cross-linking formulation consisting essentially of (1) basic lead sulfate or basic lead sulfite, (2) at least one member selected from the group consisting of Z-mercaptoimidazolincs, Z-mercaptopyrimidines, and thioureas, and (3) sulfur, if rubber is present.

BACKGROUND OF THE INVENTION (1) Field of the Invention This is a division of application Ser. No. 43,691, filed on June 5, 1970, and now Pat. No. 3,700,650.

This invention relates to a new process for vulcanizing epihalohydrin polymers. More particularly, this invention relates to a new process for vulcanizing an epihalohydrinpolymer, comprising heating said polymer in the presence of a new cross-linking formulation which will be particularly described hereinafter. As used herein, the term vulcanizing or vulcanization includes not only the process of vulcanizing epihalohydrin polymers but also the process of covulcanizing an epihalohydrin polymer with a sulfur-curable rubber. The term covulcanizing refers to the vulcanization of blends or plies of two or more polymers to produce vulcanized polymer blends or laminates. The epihalohydrin polymers mentioned herein are homopolymers of epihalohydrins, copolymers of dissimilar epihalohydrins, and copolymers of an epihalohydrin with one or more other epoxides. The foregoing definitions apply to the description of the invention hereinbelow.-

(2) Description of the Prior Art Unlike the vulcanization of epoxide polymers containing double bonds, it is believed that epihalohydrin polymers are vulcanized by the halomethyl group being the side chain of the polymer molecule.- I-Iowever, the precise mechanism involved remains yet to be fully elucidated. It is for this reason that any search for a suitable vulcanizing agent or cross-linking formulation is a quite difiicult task.

The conventional processes for the vulcanization of epihalohydrin polymers are disadvantageous, particularly, in such aspects as vulcanizing velocity, the thermal stability and non-colorability of the vulcanizate, etc.

As for any covulcanizing process for an epihalohydrin polymer-sulfur curable rubber system, the mechanism involved is more complicated than that of the vulcanization of an epihalohydrin polymer alone. Thus, it is not as easy as adding sulfur to the cross-linking formulation usable in the homo-vulcanizing process.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the invention to provide an improved vulcanizing process for epihalohydrin polymers.

It is a further object to provide a new vulcanizing process which enable epihalohydrin polymers to be vulcanized more rapidly than by conventional processes.

It is a still further object to provide a new vulcanizing process for epihalohydrin polymers, the vulcanizates being superior to the vulcanizates by conventional processes in thermal stability and/or mechanical properties.

A further object is to provide a covulcanizing method for epihalohydrin polymer-sulfur curable rubber systems, the improvements that can be realized being as set forth in the above description of the objects.

Further objects and advantages will become apparent as the disclosure proceeds.

Thus, this invention relates to a vulcanizing process which is characterized in that an epihalohydrin polymer is heated in the presence of a cross-linking formulation consisting of (1) at least one compound selected from the group consistin of basic lead sulfates and basic lead sulfites, (2) at least one agent selected from the group consisting of Z-mercaptoimidazolines, Z-mercaptopyrimidines, and thioureas, and, where said epihalohydrin polymer is covulcanized with sulfur-curable rubber, (3) sulfur.

In the vulcanizing process of this invention, which involves the use of a novel combination of compound (1) and agent (2) or, for said covulcanization, a novel combination of compound (1), agent (2) and sulfur (3), the epihalohydrin polymer is vulcanized at an unusually high vulcanizing velocity. In addition, the epihalohydrin polymer vulcanizate obtainable by the method of this invention features improvements in thermal stability and mechanical properties over those realized by the conventional methods.

BRIEF DESCRIPTION OF THE DRAWINGS The sole figure shows the relation of cross-linking time in minutes to torque in kilogram-centimeters in the method described in Examples 5 and 13, with a control relation being also shown.

DETAILED DESCRIPTION OF THE INVENTION The epihalohydrin polymers which can be vulcanized by the vulcanizing method of this invention include the homopolymers of epihalohydrins, the copolymers of dissimilar epihalohydrins, and the copolymers of any epihalohydrin with one or more other epoxides. Among the epihalohydrins are epichlorohydrin, epifluorohydrin, epibromohydrin and the like. The aforementioned other epoxides include, among others, ethylene oxide, propylene oxide; butene oxide, cyclohexene oxide, styrene oxide, butadiene monoxide, perfiuoropropylene oxide, perfluoroethylene oxide, ethylglycidyl ether, 2-chloroethylglycidyl ether, allylglycidyl ether, etc. Those polymers may be readily prepared by polymerizing epihalohydrins, or -copolymerizing epihalohydrins with the other epoxides with a catalyst which may for example be an organoaluminum compound. Particularly, effective catalysts for the polymerization of epihalohydrins or the copolymerization of epihalohydrin with other epoxides can be prepared by reacting the reaction product of a hydrocarbon-aluminum compound and a cyclic ether with an imide in the molar ratio of 110.1 to 1:1 on the basis of the hydrocarbonaluminum compound used. Epihalohydrin polymers may be obtained either in amorphous state or in crystalline state, or in the form of a varying mixture of the two forms, depending upon the methods of polymerization used and, particularly, upon the types of catalyst employed. And the vulcanizing process of this invention is applicable to any of the above polymer forms. However, in order to produce a superior rubber of epihalohydrin polymer, it is generally preferable to employ a polymer in vwhich both amorphous and crystalline polymers are present and the proportion of the crystalline polymer is in the range of about to percent. In addition, depending upon the polymerization method that may be chosen, the molecular weight of the resulting epihalohydrin polymer may be varied. And any of such polymers having varying molecular weights may be vulcanized by the process of this invention. However, in order to produce a particularly superior rubber, the molecular weight of the epihalohydrin polymer is preferably in the range of about 200 thousand to about 5 million. This molecular weight range corresponds to 1-10 dl./g. in reduced specific viscosity (RSV). The term RSV, which is a function of molecular weight, is used herein to designate the specific viscosity measured at 30 C. in a nitrobenzene solution containing 0.1 g. per 100 ml. of the polymer divided by the concentration of the solution.

Any sulfur-curable rubber can be vulcanized with one or more of the above epihalohydrin polymers in accordance with the vulcanizing process of this invention. Exemplary sulfur-curable rubbers are styrene-butadiene rubber, natural rubber, isoprene rubber, polychloroprene, acrylonitrile-butadiene rubber, isoprene-isobutylene rubber, ethylene-propylenediene terpolymer, cis-polybutadiene rubber, and cis-polyisoprene rubber, lower alkylene oxide-allylglycidyl ether copolymers such as propylene oxide-allylglycidyl ether copolymer.

In accordance with this invention, epihalohydrin polymers, or blends or plies of an epihalohydrin polymer with a sulfur-curable rubber, can be vulcanized or covulcanized by heating then in the presence of at least one of compounds (1) and at least one of agents (2) and, further, in the presence of a rubber, sulfur (3).

As has been previously stated, said compound (1) is any of the basic lead sulfates or basic lead sulfites.

We are the first to use basic lead sulfates and basic lead sulfite, in the vulcanization of rubbers. These compounds may be written as lead oxide plus a varying proportion of lead sulfate or sulfite and sometimes further plus a varying proportion of water. While those basic lead sulfates and basic lead sulfites may thus be formally written as an articulate system consisting of, for example, lead sulfate or lead sulfite, lead oxide and water, they are markedly different from those compounds, possessing entirely different physical and chemical properties as evidenced by X-ray diffraction, differential heat analysis and other analytical methods. In addition, basic lead sulfates and basic lead sulfites, unlike the formal components, or mixtures of these components, exhibit excellent vulcanizing effects when used in the vulcanization of epihalohydrin polymers. It is a particularly important advantage that with basic lead sulfates or sulfites, it is possible to obtain white vulcanizates which can hardly be manufactured with the use of conventional vulcanizing agents. As basic lead sulfates and basic lead sulfites, any di, tri and poly-basic lead sulfates or sulfites may be employed.

To cross-link an epihalohydrin polymer, any of the Z-mercaptoimidazolines having the general formula:

can be successfully used. Among the Z-mercaptoimidazolines that can thus be used are 2-mercaptoimidazoline, 4-methyl-Z-mercaptoimidazoline and 5-ethyl-4-butyl-2- mercaptoimidazoline.

For the same cross-linking purpose, any of the 2-mer captopyrimidines having the following general formula:

can be used. Among the Z-mercaptopyrimidines that can be used are Z-mercaptopyrimidine, 4,6-dimethyl-2-mercaptopyrimidine, 5'-butyl-Z-mercaptopyrimidine and 4-ethyl- 5-propyl-2-mercaptopyrimidine.

Any thiourea having the general formula:

may be employed. Thus, diethylthiourea, dibutylthiourea, trimethylthiourea, propylenethiourea may be mentioned by way of example.

The 2-mercaptoimidazolines and Z-mercaptopyrimidines are especially preferred. When an epihalohydrin polymer is vulcanized with use of such a cross-linking formulation of this invention as described above, the amount of the cross-linking formulation may be selected over a wide range with the optimum amount depending upon the type of epihalohydrin, sulfur-curable rubber present, the type of the cross-linking formulation, the desired degree of cross-linking and other factors. Usually, the amount of the cross-linking formulation may be such that the compound (1) is in the range of from about 0.1 to about 30 part(s) by weight and the agent (2) in the range of from about 0.2 to about 7 part(s) by weight, per 100 parts by weight of the epihalohydrin polymer. In case an epihalohydrin polymer is covulcanized with a sulfur-curable rubber, the amount of sulfur (3) to be added as a supplement is preferably in the range of from about 0.2 to about 7 parts by weight on the same basis.

It may be desirable, in some cases, to add auxiliary or secondary accelerators. Among such secondary accelerators are guanidines, such as diorthotolyl guanidine, thiazoles such as mercaptobenzothiazoles, and certain amine based accelerators such as butyraldehyde-aniline condensate.

In the covulcanization of an epihalohydrin-sulfurcurable rubber system, the covulcanizable composition may be either a blend or a ply. In such a covulcanizable blend, the proportion of the epihalohydrin polymer may vary over a wide range, the determining factor being the properties desired in the vulcanizate.

In general, the amount of the epihalohydrin polymer may vary within the range of from about 20 to about percent by weight of the blend. Such a blend may be prepared by any of the conventional rubber blending methods. For example, a two-roll mill may be used to blend an epihalohydrin polymer with a sulfur-curable rubber.

The components of the cross-linking composition, and the stabilizer if one is used, can be incorporated in or admixed with the polymer or blend in any desired manner. For example, they can be uniformly blended with the polymer or blend by milling in a Banbury mixer. By such a method, the cross-linking components may be evenly distributed throughout the polymer or blend.

In the case of covulcanizable plies to form laminates, the cross-linking components will be blended individually with the polymer and rubber before they are laid up. In any case, cross-linking takes place when the vulcanizable or covulcanizable composition is subjected to heat. The conditions under which cross-linking is accomplished can be varied within broad limits. Generally, the crosslinking temperature is in the range of about C. to

6 about 220 C. The cross-linking time varies inversely with Parts the temperatureand may range from about 2 minutes to The polymer 100 about 5 hours. Cross-linking is generally conducted in Zinc stearate 1 metal molds under a pressure of about to about 200 Nickel dibutyldithiocarbamate 1 atms. 5 Fast extrusion furnace black (FEF) 50 iln addition to the cross-linking components, other Cross-linking agent ingredients may also be incorporated. The additives nor- Compound (1) Varied mally employed in the vulcanization of rubber can be Agent (2) 1.5 em 10 ed for the resent ur oses. Thus, for exam 1e, usmi-y 1.. ma s varifius amdm 8.1.1. as at... 10 gggggg gqgg gegg ggag g t g g33 53;; 2:} 51: 23 3: g g gg 3 2:35 roll, 20 R m. rear roll; the front roll maintained at 10 5525;235:1213... .21 5355225212231: 2.1.1? 132252133212 .2125?as aaas azas; 15 canlzate were measure y t e me 0 s specl e y 8 ig gfii a it g igig f z iyfii fig fiz ggg: k-6300. The standard vulcanization was conducted at 155 tibn groduct of crotonaldehyd and ;-methyl6-tert- 70 kgjcma for 0 minutes and Rost'vulcanization butylphenol, nickel dibut'yldithiocarbamate, the zinc salt ggg gfii i g ig g g is lizg i ggf f gf 25.5.1255223222532:ifitiinfiifiiifi? raiser; g gg a as by those containing reinforcing fillers and antioxidants, ex- J. i; i 5 below T and EB denote tensile Strength hibit properties useful in applications requiring oil resist- (kg /cm 2) and e1 i (at break) (percent) respec 2 222 12? gf gzs i ggiggz z gg g g 82 E285; 25 tively. Percent change means the change in percentage relathere are cases in which no additive is required or desired to-the correspondmg physlcal property of the Standard I vu canlzate. zggj gg z i gz achleved wlth the crosslmkmg The vulcanizing velocities were measured with a Disk- Rheometer (built by Toyo Seiki K.K. L-rotor type rotary The followm exam les are 1ven for illustrative uro poses only It %s obvi us that many modifications and reclprocatmg moments 6 cycles per at 155 for Examples 5 and 13 and Control 4. Those velocities changes may be made wlthout departing from the scope are Shown by curves (C) (D) and (B) respectively in n 0 5 9 232 5 2: gi g g zg z is i s and claimed In the the drawing. In the measurement, the lowest torque readp p y g ing after the input of the sample was assumed to be the E l 1.45 cross-linking start time, and the change in torque (kg.cm.) was measured and plotted against cross-linking time In e followmg examples. an p q y g n ymat Basic lead sulfate (3PbO-PbSO /2H O) and hill/111g a RSV 075111116 0f 12 'F 111 f baslc lead sulfite (PbOPbSO /2H O) were used as c0mbenzene at 30 C.) was made up mto the followlng pounds (1). The results are set forth in Table 1-(i)-Table composition. 40 l-(iv).

TABLE l-(i) Standard vuleanizate Cross-linking formulation Modulus (kg/cm!) Compound (1) Parts Agent (2) TB EB 200% 300% 400% Example No Trlbasic lead sulfate.-- 8 Dlethylthiourea. 114 600 21. 4 41. 7 70.0 93.3 106 do 5 108 578 27. 3 42. 5 69. 0 92. 4 106 8 d0 102 568 26.0 38. 4 64. 0 88. 0 99. 1 2 2-mercaptoimldazo1ine.. 370 30. 4 54. 3 100 118 5 -do 158 250 47. 6 92.5 148 8 do 149 227 43. 3 77. 9 141 5 Trlmethylthiourea- 132 395 27. 3 59. 7 106 126 --d0 5 Hexamethylene diaml e carbamate 167 355 36.0 64.7 129 Basie lead sulfit 2 Diethylthiourea 106 555 30. 5 42. 0 75. 0 73. 4 101 do 5 -d0 89.8 513 28.5 39.6 66. 4 85.4 89.4

TABLE l-(li) Standard vulcanizate Cross-linking formulation Modulus (kg/cm!) Compound (1) Parts Agent (2) TB EB 50% 100% 200% 300% 400% Example No.:

11 Basic lead sulfite 8 Diethylthiourea 85. 9 514 29.5 38.8 12 --do 2 2-mercapto1mldazoline--. 146 373 29. 8 37. 4 5 do 151 285 35.8 66.7 8 -..do 159 247 37.5 75.0 5 Trimethylthiourea 412 26. 0 49. 8 16 5 Hexamethylene dlamine carbamate 166 341 30. 8 63. 1 Control No.:

1 Lead ulfide 5 2-mercaptoimidazo1lne 123 335 23. 0 38. 9 2 Lead chromate 5 do 144 337 33. 0 66. 8 3... Lead metaborate... 5 128 228 26.2 46. 1 4 None 0 o 126 290 None-. 0 Hexamethylene dlamlne carbamate 148 481 33.4 53.8

TABLE I-(iii) Post-vulcanizate Aged vulcenizate En Modulus (kgJcmfl) Tn Ea Modulus (kg/cm!) (percent (percent (percent change) 50% 100% 200% 300% change) change) 50% 100% 200% TABLE l-(iv) Post-vulcanizate Aged vulcanizate T E}; Modulus (kg/em!) Tn En Modulus (kg/cm?) (percent (percent (percent (percent change) change) 50% 100% 200% 300% change) change) 50% 100% 200% The aging test was carried out at 150 C. for 192 hours.

Examples 17-2.1 TABLE 4 Epichlorohydrin polymer RSV 12 as determined in Control o N0. Example N0. mtrobenzene at C.) and styrene-butadlene rubber (Japan Synthetic Rubber, Ltd., TSR-ISOO) were covul- Physmlpmpertles 1 2 17 18 19 21 canized. A master batch of epichlorohydrin polymer was Tensile strength (kg/cum)--- 28.1 33.5 171 55.4 43.6 73.9 47.5 Percent change 76 57 -3.4 73 78 60 76 prepared by milling 100 parts of said epichlorohydrin E tb k t 17 17 100 10 w 20 10 polymer, 50 parts FEF carbon black and, 1 part of zinc onga mm m (Damn) stearate at -6070 C. for 10 minutes. In a similar manner, 100 parts styrene-butadiene rubber, 50 parts FEF we claim:

carbon black and 1 part zinc stearate were milled to pre- A process f vulcanizing a Polymer of an 1 pare a master batch of SBR. The above master batches hydrin i h comprises heating said polymer at about were mixed on the two-roll mill for 5 minutes, at the end to about 0 C under a pressure of about 10 to of which time val:ious additives were added The final about 200 atmospheres in the presence of a cross-linking COmPOFitiOHS are glven Each mlxture was formulation until vulcanized, said formulation essentially the! mllled for about 5 mmutesconsisting of about 0.1 to about 30 parts of a lead com- The Physical propefties of the vulcanizates are Show? pound selected from the group consisting of basic lead 19 Table 9 Physlcalo Propertles of the Same Vulcan? sulfate and basic lead sulfite, and of about 0.2 to about Zates after 8 8 at 150 for 72 hours are ShQWn 7 parts of a sulfur-bearing agent selected from the group Table consisting of a Z-mercaptoimidazoline, a Z-mercaptopyrim- TABLE 2 idine, and a thiourea, said parts being by weight per 100 Control parts of said epihalohydrin polymer.

No. Example No. 2. A process according to claim 1, wherein said epi- Recipe 1 2 17 18 19 20 21 halohydrm polymer 1s a polymer of epichlorohydnn. E 11 h dd 1 50 50 mo 50 50 25 '3. A process according to claim 1, wherein said epic or y npo ymer Sfymnemumdiem 50 50 50 50 75 100 halohydnn polymer 1s a copolymer of ethylene oxide and Tribasie sulfate" r 0 5. 0 epichlorohydnn. s gff gfi g g gg 4. A process according to claim 1, wherein said agent FEF-carbon bla 0 1s a Z-mercaptornudazolme.

I2 5. The process of claim 1, wherein said agent is a Zinc oxideTi m h with! .5 thiourea.

L0 L0 L0 L0 L0 L0 L0 6. A process as set forth in claim 4, wherein said lead s ur 1.5 1.5 1.0 1.5 1.5 1.8 2.0 compound 1s basic lead sulfite.

7. A process as set forth in claim 6, wherein said sulfur-bearing agent is Z-mercaptoimidazoline, and said poly- TABLE 3 mer 1s a polymer of epiohlorohydnn. cggglol Exam 19 No 8. A process as set forth in claim 1, wherein said lead p compound is basic lead sulfite. P y properties 1 2 17 18 19 21 9. A process of vulcanizing a polymer of epichlorohygf ti t g i k 1 t Q 33g 2 3 2% drlnbwhlch comprises heating said polymer at about 100 onga one rea percen 5 Q Modulus at 50% (kgJcmJ)- 13.7 10.1 37.6 41.5 18.5 30.3 14.8 out 220 under a pressure of abou-t 9 to about fi g p 583%, gg y g g g, &2 h)? 3; 1 atmospheres 1n the presence of a cross-llnlung formu. 0 uuse g. cm. Modulus at 300% (kg/MAL" 8M 52' 4 162 m 134 ation until vulcanized, said formulatlon essentially con sisting of about 0.1 to about 30 parts of basic lead sulfite 9 10 and of about 0.2 to about 7 parts of Z-mercaptoimidazo- WILBERT J. BRIGGS, SR., Primary Examiner line, said parts being by weight per 100 parts of said polymer. US. Cl. X.R.

References med 156-306; 161184, 239, 247, 255; 260-2 A, 2EP, 3, UNITED STATES PATENTS 5 37 EP, 41.5 R, 45.9 NC, 45. 9 P, 45.95, 37 AL, 836, 837 R, 3,341,491 9/1967 Robinson et a1 260-2 A 888, 897 R 2,996,473 8/1961 Cain et a1 -26079 Patent No. 3,8 2,241 Dated July 2, 1974 Inventor) HIIMII nu I1. All

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Ia"tho heading, utter "261,040" (6th line after the title) insert I 4 Claims priority, applioation Japan, June 12, 1969, /45,749:

80,12. 5, 1969, 44/),411: (Mt. 14, 1969, Mir/81,5657 Wit. 2.; 169, 44/l5,6737 Dec. 9, 1969, 44/98,363

Signed and sealed this 5th day of November 1974,

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHAL L DANN Attesting Officer Commissioner of FORM PC4050 (10-69) USCOMM DC 603766569 U454 sovsnumzur PRINTING omcz new o-aee-ssa. 

